Why is knowing about absorption, distribution, bioavailability and other obscure crap important?

Absorption can be affected by food. Knowing how much of a difference it makes when you take a med after eating vs. on an empty stomach may not seem like a big deal, until you can’t eat much of anything.

Say if you got very sick

Or had gastric bypass surgery

Or the med makes you want to puke when you take it on an empty stomach

Bioavailability and distribution explain why some meds are vastly more potent than others (e.g. Paxil and Prozac), but there’s not a lot of difference in their dosages.

Bioavailability made simple: practically all injected drugs are about, if not absolutely 100% bioavailable.
As most of the drugs we deal with here are taken orally (even if they do have an injectable version available), the simple version of bioavailability usually isn’t an option. So what do you need to know about bioavailability? Unless you’re studying to be a pharmacist or doctor, or you just like to learn everything you can about a med, you don’t need to know any of this.
Except when there’s a problem with a generic medication, and you want to figure out what the hell is wrong14. Not that you could do anything about it, or that the data on the generic medication are readily available, but it’s nice to know that the problem isn’t in your head. Rather the generic med in question doesn’t act the same way as the brand or another generic somewhere between your stomach and your brain. The most notorious example of this to date is Teva’s Budeprion XL version of Wellbutrin XL. We go into great detail about it in the section on branded vs. generic drugs, with an example of how these data are used.
The plasma half-life is the same as above and repeated here just to make it easier to perform any calculations you may want to do.

However, the FDA requires only a single, frequently sub-therapeutic dose taken by healthy volunteers to test pharmacokinetic data, including bioavailability and bioequivalence factors. Until recently all pharmacokinetic data for a drug were based on a single study done on fewer than 20 healthy volunteers, who were mostly, if not all white males between the ages of 20 and 50 willing to take recently developed drugs because they need the money. Those guys took a single dose, which was often lower than the typical starting dosage, on an empty stomach, first thing in the morning. The only way to tell if the data is from the real world (e.g. from people with the condition the med treats who are in stage III clinical trials) is to look at the pharmacokinetics section of a drug’s Full US PI sheet, or some of the better overseas equivalents. If it doesn’t tell you how many people participated with demographic data, assume it was a handful of healthy white guys desperate for cash.
You can probably tell how those crappy studies create a big problem with pharmacokinetic data.

Fortunately more and more pioneering pharmaceutical companies (the ones that make the original, brand-name drugs) are using far more people in their studies, including those with the conditions as well as healthy volunteers to determine all PK data, they are not required to do so. By the US FDA. Other countries have different standards, and that forces big pharma to provide better PK data.
But unless a it’s a completely new drug that has been approved recently, or an existing drug that has been recently approved for a very different application, including overseas approvals, the PK data are probably from a dozen white guys who needed the money.

Keep Crazymeds on the air.
Donate some spare electronic currency
you have floating around The Cloud

11 See footnote 2 above. The good news is generic manufacturers are required to be at least 90% sure of everything being within the 80–125% range.12 If we see any evidence of a generic manufacturer ever doing more to establish the 80–125% bioequivalence standard than giving one small dose of the med to the 20 white guys who have already sold their monthly allotment of plasma, we’ll note it.

12 I know that’s not what a 90% confidence interval really means, but sometimes that’s what it seems like. Which is why we list all known generics (if any are available) that have been independently verified to meet the 80–125% standard on {{$$brandname}}’s Expanded Brand & Generic page.

All drug names are the trademarks of someone else. Look on the appropriate PI sheets or ask Google who the owners are. The way pharmaceutical companies buy each other and swap products like Monopoly™ real estate, the ownership of any trademarks may have changed without my noticing.

All rights reserved. No warranty is expressed or implied in this information. Consult one or more doctors and/or pharmacists before taking, or changing how you take any neurological and/or psychiatric medication. Your mileage may vary. What happened to us won’t necessarily happen to you. If you still have questions about a medication or condition that were not answered on any of the pages you read, please ask them on Crazy Talk: the Crazymeds Forum.
The information on Crazymeds pertains to and is intended for adults. While some information about children and adolescents is occasionally presented (e.g. US FDA approvals), pediatric-specific data such as dosages, side effects, off-label applications, etc. are rarely included in the articles on drugs or discussed on the forum. If you are looking for information regarding meds for children you’ll have to go somewhere else. Plus we are big pottymouths and talk about S-E-X a lot.Know your sources!Nobody on this site is a doctor, a therapist, or a pharmacist. We don’t portray them either here or on TV. Only doctors can diagnose and treat an illness. While it’s not as bad as it used to be, some doctors still get pissed off by patients who know too much about medications, so tread lightly when and where appropriate. Diagnosing yourself from a website is like defending yourself in court, you suddenly have a fool for a doctor. Don’t be a cyberchondriac, thinking you have every disease you see a website about, or that you’ll get every side effect from every medication1. Self-prescribing is as dangerous as buying meds from fraudulent online pharmacies that promise you medications without prescriptions.
All information on this site has been obtained from the medications’ product information / summary of product characteristic (PI/SPC) sheets and/or medication guides - which is all you get from sites like WebMD, RxList, NAMBLA NAMI, etc., the sources that are referenced throughout the site, our personal experience and the experiences family, friends, and what people have reported on various reputable sites all over teh intergoogles. As such the information presented here is not intended as a substitute for real medical advice from your real doctor, just a compliment to it. You should never, ever, replace what a real doctor tells you with something from a website on the Internet. The farthest you should ever take it is getting a second opinion from another real doctor. Educate yourself - always read the PI/SPC sheet or medication guide/patient information leaflet (PIL) that comes with your medications and never ever throw them away. OK, you can throw away duplicate copies, but keep at least one, as that’s your proof of purchase of having taken a med in case a doctor doubts your medical history. Plus they take up less space than a bottle, although keeping one inside of a pill bottle is even better.
Crazymeds is not responsible for the content of sites we provide links to. We like them, or they’re paid advertisements, or they’re something else we think you should read to help you make an informed decision about a particular med. Sometimes they’re more than one of those things. But what’s on those sites is their business, not ours.
Very little information about visitors to this site is collected or saved. From time to time I look at search terms used and which pages they bring up in an effort to make the information I present more relevant. And the country of origin, just because I’m geeky like that. That’s about it. Depending on how you feel about Schrodinger, our privacy policy should either assuage or exacerbate your paranoia.
Crazymeds is optimized for ridiculously large screens and browsers that don’t block ads. I use Firefox and Chrome, running under Windows 72. On a computer that sits on top of my desk. With a 23 inch monitor. Hey, at least you can make the text larger or smaller by clicking on the + or - buttons in the upper right hand corner. If you have Java enabled. Like 99% of the websites on the planet, Crazymeds is hosted on domain running an open source operating system with a variety of open source applications, including the software used to display what you’ve been reading. As such Crazymeds is not responsible for whatever weird shit your browser does or does not do when you read this site3.
No neurologists, psychiatrists, therapists or pharmacists were harmed in the production of this website. Use only as directed. Void where prohibited. Contains nuts. Certain restrictions may apply. All data are subject to availability. Not available on all mobile devices, in the 12 Galaxies Guiltied to a Zegnatronic Rocket Society, or in all dimensions of reality. Hail Xenu!

1 While there are plenty of books to help you with hypochondria, for some reason there’s not much in the way of websites. Then again, staying off of the Internetis a large part of curing/managing the disorder.

2 Remember kids, Microsloth operating systems are like TOS Star Trek movies with in that every other one sucks way, way more. With TOS Star Trek movies you don’t want to bother watching the odd-numbered ones. With Microsloth OS you don’t want to buy and install the even-numbered ones. Anyone who remembers ME and Vista knows what I mean.

3 Have I mentioned how open source operating systems for commercial applications is one of the dumbest ideas in the history of dumb ideas?* I don’t even need my big-ass rant any more. Heartbleed has made my case for me. And that’s just the one that got all the media attention. The very nature of an open source operating system makes security as much of an illusion of anonymity. Before you flip out too much: the domain Crazymeds is hosted on uses a version of SSL that is not affected by the Heartbleed bug. That’s one of the many reasons why I pay a lot of money and keep this site on Lunarpages.

* Yes, I know I’m using open source browsers. I also test the site using the now-defunct IE and Safari browsers. Their popularity - and superiority - killed IE and Safari, so that’s why I rely on the open source browsers. It’s like brand vs. generic meds. Sometimes the generic is better than the brand.